Electric horn



latented Mar. 11, 1930 UNITED STATES PATENT yOFFICE FABNM IF'. DORSEY,0F ROCHESTER, NEW YORK, ASSIGNOR, BY MESNE ASSIGNMENTS,

TO NORTH EAST APPLIANCE CORPORATION, OF ROCHESTER, NEW YORK, A. COR-PORATION OF NEWYORK .ELECTRIC HORN v Application led July'IO, 1925.Serial No. 42,780.\

1,729,281 to William B. Connolly, in which an overtone is produced bythe independent res- -onant vibration of the armature by which thediaphragm ismagnetically actuated.

The object of the invention is tovincrease the eiliciency and facilitatethe manufacture of horns of this type, and this is accomplished by theuse of a magnetic and sonorous armature of the form hereinafterdescribed.

In the accompanying drawings, Fig. 1 is a side elevation, partly insection, of an electric horn embodying the present invention. Fig. 2 isaside elevation, in section approximately on the line 2-2 in Fig. 3. Fig.3 is a front elevation of a portion of the horn comprising the rearshell, or housing, and the parts attached thereto and enclosed therein.Fig. 4 is an elevation, partly in section, of the circuit-breaker andthe' parts immediately associated therewith.

The invention is illustrated as embodied in a horn having an elasticmetal diaphragm 5, which is gripped and supported, at its margin,betweena front plate 6 and a cup-shaped metal shell or housing 7.Attached to the front plate 6 is the horn proper or projector 8, whichmay vary in lengthaccording to the pitch of the note which 1t is desiredto produce. The front plate and the housing are secured togetherv by`bolts 9.

The electromagnet comprises a central core 10, which is surrounded by acoil or windin 11. It comprises also a generally U-shape yoke 12 formedof a relatively wide and thin strip of steel, with its extremities bentin wardly, as shown in Fig. 1. The housing and the yoke, are centrallyperforated, and the core has a screw-threaded rearwardly projectingextremity 13,- which passes through these members and receives a nut 14y which the parts may be all drawn and secured tightly to ether. Thecoil, being embraced by the yo e and particularly by its inturnedextremities, is securely fixed in place in a simple and eiective manner.The part 13 of the core is attened, or otherwise vmade non-circular incross section, and the openings in the yoke and the housing arecorrespondingly formed, so that these parts are prevented fromaccidental relative rotation, while the-original assembly of the partsis facilitated.

The armature, which cooperates with the electromagnet, consists chiel ofa relatively wide and long bar 15. This har is secured to the middle ofthe diaphragm by a bolt 16, the necessary space between the armature andthe diaphragm being. maintained by a sleeve or spacer 17 surrounding thebolt. The bolt is made of steel, so that its head 18,y lying at the rearof the armature, may be considered as a part of the magnetic circuit,cooperating with the core 10. The circuit iscompleted through thearmature and through the lateral members of the yoke, the magnet thushaving three poles, all separated by suitable air-gaps from thearmature.

In the present construction the principal, or lower, tone of the hornhas a pitch due to the relation of the stiffness of the diaphragm to thetotal load or weight upon the diaphragm. The overtone results fromvibration of a higher frequency, imposed also upon 75 the diaphra m, andresulting from local vibrations in t e armature. In order that theselocal vibrations may be emphasized as much as possible, the armature bar15 is made longer than necessary to perform its magnetic function,extending substantially beyond the outer poles of the magnet, as shownin Fi 1. For the same reason it is preferably ma e thicker than necessarfor the magnetic function, and in order t at this thickness may not giveit a rate of vibration too high for the intended purpose, the bar isreduced in thickness for limited portions 19, adjacent its pointof at-`tachment to the diaphragm. This may be tion may be free, the air-gapsbetween the Aarmature and the outer poles of the magnet are madesomewhat greater than the gap at the core, so that no engagement occursbe- 10o tween the armature and the ends of the yoke. ward direction, soas to cause the contacts to The motion of the diaphragm is accordinglythe resultant of the relatively slow vibrations, due to its own naturalfrequency and the load upon it, and the relatively high vibrationstransmitted to it from the armature, while the ehect, in accordance withwell known phonetic laws, is that of two distinct harmonious tones.

The circuitbreaker, by which the current through. the winding 11 iscontrolled and rendered intermittent, comprises a normally staticnarycontact 20, and a movable contact 21 cooperating therewith. The movablecontact is mounted on a blade spring 22, and this spring projects, atone extremity, into the path of movement of the armature, so that ateach rearward vibration of the latter the spring is engaged and pressedrearwardly, thus separating the contacts. Where it is desired toinsulate both sides of the circuit from the mass of the horn` a piece otinsulating material 23 is attached to the end ot the bladespring toprevent direct metallic engagement between tue armature and the spring.

ln order that the circuit-breaker may be conveniently adjusted toregulate the current impulses in the magnet, the contact 20 and theblade-spring 22 are mounted upon asupport in the form of a sheet-metalplate 2d, being insulated therefrom in any convenient manner. The plateis bent rearwardly at its lateral edges, so as to provide parallel arms25, continuous with tlangcs 32. it its rear edge the plate has tworearward projections 2G, which rest against the inner surface of thehousing, as shown in Fig. 3. T he plate cooperates witha base-member,formed also ot sheet-metal and comprising a horizontal portion 27 and avertical portion 28 (referring to Fig. Two lugs 41, projecting from thehorizontal portion, are riveted to the housing to secure the base inplace. The horizontal portion is cut away at its forward end, as shownparticularly in Figs. 2 and li, and formed with lugs 29 which overhangthe projections 26 on the plate 24, and thus, through the reaction ofthe springs and other parts hereinafter described, prcjviding pivotalbearings about whichthe platel may swing on a line adjacent the innersurface vof the housing, and in the general direction of movement of thediaphragm and the armature.

At its inner extremity the part 28 of the base is provided with twoforwardly bent projections 30, which constitute supports for coiledsprings 31, ressing at thelr forward ends against the anges 32 on theplate 24. The arms 25 rest against the outer surface of a bar 33 intowhich an adjusting screw 34 is threaded, and this screw projects throughan opening in the wall of the housing, so that it is accessible from theoutside and may be turned by a screw-driver. The gprings 31 tendnormally to rock the plate 2a in a forcbe separated earlier in eachrearward motion of the armature. This tendency of the springs isresisted, however, by the arms, the cross-bar and the adjusted screw;and by rotation of the latter the operative position of thecircuit-breaker may thus be exactly determined, while the constantpressure of 'the springs 31 not only preventsany accidental movement,but also acts to thrust the projections 26 outwardly and hold them ineective engagement with the housing and with the lugs 29.

The blade-spring, the stationary contact., and the terminals by whichthey are connected with other parts of the instrument, are secured tothe plate 24 by means of screws 37.' Two bindingposts 38 project throughthe walls of the housing and serve to connect the horn with the exteriorparts ot its energizing circuit. A. condenser 39 is connected with thetwo contacts of the circuit breaker for the usual purpose, as aconvenient means for supporting this condenser, it is attached to themiddle ot a strip 420 of insulating material, and this strip is securedin place by 'the nuts and washers on the inner ends of the bindingposts, as shown in Fig. 3.

rl`hc invention claimed is:

1. ln an electric horn, the combination, with a sonorous diaphragm andan electromagnet, ot a resonantly vibratory armature attached, at itsmiddle point only, to the mid dle of the 'diaphragm and cooperatingmagnetically with the magnet, the armature being relatively thick andrigid 'for the greater part of its length, but having limited portionsot reduced thickness close to itspoint of attachment, whereby resonantbending ot the armature is substantially restricted to the parts thereofadjacent the point o attachment.

2. ln an electric horn of the type in which a resonantly vibratoryarmature is attached, at its middle point only, to a sonorous diaphragm,an armature in the form of a bar provided with two parallel transverseslots located near to and on opposite sides of its point of attachmentto the diaphragm, whereby the resonant bending of the armature issubstantially limited to the positions in which the thickness is reducedby the slots.

FARNUM F. DORSEY.

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